DESCRIPTION (from applicant's abstract): The mammalian olfactory system requires that dying olfactory neurons (OSNs) and other epithelial cells be replaced to maintain proper function. Indeed, failure of epithelial reconstitution is a major cause of human olfactory dysfunction. Little is known in detail regarding reconstitution of the olfactory epithelium (OE) after injury. Globose basal cells (GBCs), a rapidly proliferating pool of progenitors found in the OE, include cells that act as immediate neuronal precursors. However, in some settings, a subset of GBCs function as multipotent progenitors and can give rise to both OSNs and non-neuronal cells. Thus, the reconstitution of the epithelium and the specific regeneration of neurons are dependent on elements that control GBC fate determination. The Notch signaling pathway is a form of cell-cell communication important for cell fate determination. Considering the extent to which the Notch pathway is used throughout development, the Notch pathway would be an appropriate mechanism for regulating either GBC fate determination or OSN differentiation. In normal OE, neurons are generated at a relatively low rate in contrast to the high rate after ablation of the olfactory bulb (OB) and to the high rate of both OSN and non-neuronal cell after methyl bromide (MeBr) lesion. We hypothesize that the Notch pathway will subserve some of the differences in GBC cell fate in normal versus lesioned OE. We intend to identify the cell types that express Notch pathway genes and the extent to which each factor is expressed in normal, OB-ablated and MeBr-lesioned OE using an interlocking web of techniques: reverse transcriptase-polymerase chain reaction, ribonuclease protection assay, in situ hybridization and immunohistochemistry. In order to examine function of rat Notch 1 on GBC fate determination in vivo we will use a replication incompetent retrovirus containing a dominant negative construct and another encoding a constituitively active construct. We hypothesize that the constituitively active form of Notch 1 will lead to a reduction in the regeneration of OSNs and conversely, the dominant negative form of Notch 1 will cause an excess of OSNs. We intend to describe the functional effects of aberrant Notch 1 expression in normal, OB ablated and MeBr-lesioned OE by assessing the phenotype of the infected cells using a panel of epithelial cell marker antibodies. The knowledge gained from these experiments is important when investigating potential therapies to alleviate human olfactory dysfunction.